Pulse tube method of refrigeration and apparatus therefor



March 1, 1966 w. E. GIFFORD 3,237,421

PULSE TUBE METHOD OF REFRIGERATION AND APPARATUS THEREFOR Filed Feb. 25,1965 2 Sheets-SheetI 2 Iaweabw.- WZZd'azzEGaffavd, y www H'aaraqy UnitedStates Patent O 3,237,421 PULSE TUBE METHOD F REERIGERATION ANDAPPARATUS THEREFR William E. Gifford, 829 @strom Ave., Syracuse, N.Y.uned rieb. 25, i965, ser. No. 435,174 13 Claims. (Cl. 62-88) The presentinvention is a continuation-in-part of application Serial No. 279,379,filed May 10, 1963, now abandoned.

This invention relates to an i-mproved method and apparatus forproducing refrigeration and, more particularly, to a method of laminarow cooling in which very low temperature refrigeration is achieved bymeans of an oscillating pressure exerted in a gas filled tubularenclosure. The pressurized volume of gas is controlled so as to move in.and out of the tubular enclosure with lamina flow parallel to the axisof the tubular enclosure and there is thus set up #a novel heat exchangemechanism, whereby a significant temperature gradient may becontinuously induced in the tubular enclosure.

The method of the invention is hereinafter referred to as Pulse TubeRefrigeration and the apparatus is referred to as a Pulse TubeRefrigerator. The invention has for its principal objective theoriginating of a new concept of cooling and the embodying of thisconcept in one or more practical working forms whereby usefulrefrigeration in a range of very low temperatures may be realized.

Another object of the invention `is to provide an improved method ofrefrigeration which utilizes an apparatus having a minimum number ofmoving parts capable of achieving relatively low temperatures withoutbeing subect to problems relating to Wear, faulty sealing, valvefailure, and the like.

Another objective is t0 devise an apparatus of the character describedwhich is of relatively high efficiency which is capable of being carriedon in multi-stages so that progressively induced cooling may beaccomplished to realize refrigeration at very low temperatures withrelatively inexpensive equipment.

The nature of the invention and its other objects and novel featureswill be more fully understood and appreciated from the followingdescription of preferred embodiments of the invention selected forpurposes of illustration and shown in the accompanying drawings, inwhich:

FIGURE l is a diagrammatic view of one simple form of pulse tubeapparatus by means of which a gas may be compressed, heated, and thenexpanded with a net cooling taking place and a continuous temperaturegradient being induced;

FIGURE 2 is a diagrammatic View in graph form showing the changes thegas undergoes in order to achieve refrigeration at temperatures lowerthan room `temperature;

FIGURE 3 is a diagrammatic View of another form of pulse tube of theinvention in which portions of the pulse tube is shown in cross section;

FIGURE 4 `is a modified form of apparatus of the in- 1 vention includingmulti-stage pulse tube cooling units by means of which progressivelylower temperature may be achieved;

FIGURE 5 is a fragmentary `cross sectional view of `a pulse tube andheat exchanger construction; and

FIGURE 6 is a detail cross sectional view taken approximately on theline 6 6 of FIGURE 5.

The method of puise tube refrigeration of the invention is, in general,based upon the concept of a novel heat exchange mechanism which operatesto provide both a cooling effect in a first part of a confined space anda heating effect in a second part of said confined space in ICC such amanner that heat is pumped from the first part to the second part.

In accordance with the invention method, oscillating pressure is exertedon a gas confined in a tubular enclosure and the pressurized volume ofgas is caused to move in and out of the tubular enclosure in a laminarow pattern parallel to the axis of the tubular enclosure. The coolingeffect noted above is accomplished at one end of the tubular enclosureand the heating effect noted above takes place at the opposite end ofthe tubular enclosure. As a result of these two effects a significanttemperature gradient may be continuously induced in the tubularenclosure where heat is being pumped from the cold end to the hot end.

The method of the invention in one simple form is illustrateddiagrammatically in FIGURE l. As shown therein an enclosed volume 2 isconnected to a source of compressed air or other gas from a compressor 4by conduits 6 and 8 which are fitted with suitable valve means 10 and12. A heat exchanger 14 is located at one end of volume 2 and ismaintained by suitable cooling means 1S at a constant temperature asroom temperature. It should be understood that there may be employedanother heat exchanger in the entrance end of the tubular encloure 2.

In operation, -gas under pressure from the Source 4 is supplied throughvalve 10, while valve 12 is closed for a short interval (a second orless) in which the gas vc-lume in the enclosure 2 is compressed andheated. Heat of the compressed volume of gas at the further end of thevolume 2 is transferred to the heat exchanger 14. Any gas may be used inthe refrigeration method which remains a gas throughout the temperatureand pressure range of the desired cooling operation. For example, aircan be used down to K.; hydrogen can be used down to 30 K., and heliumcan be used down to 6-8 K.

Immediately thereafter the gas from which heat iS removed is returned byclosing valve 10 and opening valve 12. This allows gas returning fromthe heat exchanger to expand and as this occurs the portion of gas thusexpanded tends to cool to a lower temperature than it was at when itentered the valve 10; Thus it will be apparent that when heat is removedfrom the heat exchanger 14, by cooling means 15, it becomes feasible toexhaust gas at a temperature lower than the temperature of the gas as itenters volume 2.

This illustrated diagrammatically in FIGURE 2 wherein Ti indicatestemperature of -a portion of gas as it enters volume 2; Tc is thetemperature of a compressed portion of the gas; Ts is the temperature ofthe gas after giving up heat to the heat exchanger 14; and To istemperature of gas after it returns and becomes expanded.

In order to produce refrigeration more efficiently and at much lowertemperature than that possible with the device of FIGURE 1, I may employa further arrangement of this general nature as shown, for example, inFIGURE 3 wherein I have indicated an enclosed volume 2' in which isprovided a heat exchanger 14 and also -a second flow smoothing heatexchanger 14a. Gas is furnished from a compressor 4 through conduits 6and S controlled by volumes 10' and 12 and also through a regenerator2f). Gas is conducted from the regenerator 20 through conduit 2da t-othe lower side of heat exchanger 14a.

The heat exchanger 14 is located in the confined end of enclosed volume2' and may be of a conventional type and operates in the usual manner.The flow smoothing heat exchanger 14a is located at the entrance end andperforms two functions. It gives up heat to the exhausting gas andbecomes cooled, and it causes all the gas to move in the tube withlaminar flow parallel to the axis of the tube. Some portions of the gasmove different distances than other portions in the tube but in parallelpaths of travel without turbulent mixing with one another.

I have determined that pulsing movement of the gas in the mannerdescribed above may, for example, be accomplished by travelling portionsof the gas through a flow smoothing heat exchanger having Iamultiplicity of substantially uniformly sized passages each of which ischaracterized by substantially equivalent functional flow resistance.

The heat exchanger 14a comprises one desirable means of thus inducinglaminar flow in a tubular enclosure and includes a `chambered base and anovel porous body 14C which may, for example, consist of a sinteredmetal produced from metal particles having binder coated surfaces. Thisarrangement is shown in detail in FIGURE and as noted therein 14Cdenotes the sintered bronze portion of heat exchanger 14a formed in theshape of a cylindrical layer or disc. This body is fitted inside thetubular enclosure 2 and is solidly bonded at the upper side of the basecomponent Mb. The base Mb is formed with chamber 14d into |which gas issupplied from the compressor 4 through a conduit 20a. The base 14h ispreferably comprised of a metal such as lcopper and is further formed atits upper portion with a number of openings as 14e, lef, 14g, etc. whichcommunicate with the porous undersurface of the sintered metal disc andthus provide for circulating a flow of gas into and through the sinteredbody at substantially all points therearound.

The sintered body Mc provides a multiplicity of substantially uniformlysized passageways each of which are characterized 'by substantiallyequivalent frictional flow resistance which may be desirably employed toinduce a positive laminar flow pattern of gas inside the tubularenclosure. It is pointed out that gas is supplied under pressure throughthe passageway 14n and then into the openings 14e, 14]c and 14g in aturbulent state. As it passes through the multiplicity of openings inthe sintered body the flow of gas is smoothed out and travels alongparallel paths of flow both inwardly and outwardly as indicateddiagrammatically by the arrows V and W in FIGURE 5 and a laminar flowpattern is thereby produced.

IFlow of compressed gas from compressor 4 is controlled by valve l0 and12. Located between the heat exchanger 14a in the volume 2 and valve 10and l2 is a regenerator 20. The valves l0 and I2 are regulated to letgas in and out of the regenerator and heat exchanger 14a giving uprefrigeration as the gas expands at the end of the volume 2 where theheat exchanger 14a is located.

As the gas expands it may absorb heat from any desired heat load. In thedrawings one typical heat load is diagrammatically indicated by thememberl Q which can, for example, be a solid body or a conduit forreceiving therethrough `a fluid body.

The tube Wall along its length in the direction from 14a to 14 varies intemperature between certain limits. Each of the wall temperature valuesremain essentially constant. The gas, however, as it moves along thewalls changes in temperature as a function of pressure.

As noted above a novel heat exchanger mechanism is set up to providetransfer of heat from the entrance end of the volume 2 to the far end.This is due to a heat exchange between the gas in the tube and the wallsof the tube. When the gas is at high pressure it is hotter than the tubewall all along the tube and a heat transfer from gas to wall occurs.When, however, the gas is at low pressure the temperature of gas islower than that of the tube wall and a heat transfer all along the tubefrom wall to gas occurs.

However, the quantity Q of heat picked up by a corresponding smallportion of the gas is transferred back t-o the wall at a location on thetube further along the tube towards the heat exchanger I4 at theopposite end thereof. In this way heat is pumped from the flow smoothingheat exchanger 14a to the heat exchanger 14 in the far end of the tube,thus providing an increased refrigerating eiict at the flow smoothingheat exchanger 14a, and also providing an increased heating efect at theopposite end heat exchanger 14. This is best achieved when the flow ofgas in the tube is essentially laminar in nature. Thus all the surfacesof the chamber walls serve in the same capacity as heat exchangers Maand 14. By this means heat may be pumped against a large temperaturedifference between the tube ends even though the pressure fluctuation isso small that no gas portion is moved all the Iway through the distancebetween the heat exchangers 14a and 14.

In FIGURE 4 there is illustrated another form of the inventionconsisting of a -multi-stage unit. As shown therein numeral 23 denotes apiston driven by a crank C mounted for reciprocation in a cylinder 24.This arrangement may be employed to move gas into an out of an enclosedvolume in the same general manner as accomplished by the valves 10 andIZ of FIGURES l and 3. FIGURE 4 also illustrates one suitable way ofinterconnecting a plurality of systems like that of FIGURE 3 in order toobtain progressively lower temperatures. Raising and lowering pressureoccurs simultaneously in successive stages. The additional stages `donot require any additional low temperature moving parts but involve onlyadditional volumes, heat exchangers and regenerators.

Considering FIGURE 4 more in detail, the piston 23 provides a ow ofcompressed gas through conduit 25 into a first regenerator 26a. Aportion of the gas moves through the conduit 27 and then through asecond regenerator 26h. Another portion of the gas moves through abranch conduit 29 and a fluid smoothing heat exchanger 30a to a firstenclosed volume 28a. At the opposite end of volume 28a is a hot end heatexchanger 32a which is cooled by suitable cooling means 34.

A compressed portion of the gas is heated and gives up heat to the hotend heat exchanger 32a. Thereafter, this portion of gas expands andIbecomes cooled as it passes through the ow smoothing heat exchanger 30aand is at a temperature lower than the temperature at which it enteredvolume 28a. This produces a refrigerating effect on heat exchanger 30a.This refrigeration may then be used by connecting a thermal conductingelement 37a to the heat exchanger 30a above-noted and to a heatexchanger 32h in a second enclosed Volume 28h, to precool heat exchanger3211 to a temperature lower than the reference room temperature.

Volume 28b operates in a similar manner to volume 28a except that thegas entering its cooled end ow smoothing heat exchanger 30h throughconduit 31 and ultimately heat exchanger 32b has been precooled furtherby regenerator 2Gb. A thermal conducting element 37b connects with anenclosed volume 28C.

Volume 28C also operates similarly to volumes 28a and 2819 except thatgas which is to enter cooled end flow smoothing heat exchanger 30C andultimately hot end heat exchanger 32C rst passes through regenerator 26Cwhere it is further cooled. A thermal conducting unit 37C connects witha fourth enclosed volume 28d.

Volume 28d again operates similarly except that gas entering flowsmoothing heat exchanger 30d and hot end exchanger 32d through conduit39 is still further cooled by regenerator 26d. A thermal conductingelement 37C connects with heat exchanger 32d.

It should be observed that the gas flow through the system is notinterrupted by any valve except the one inlet and the one outlet valveshown in FIGURES 1 and 3 and with respect to FIGURE 4 a free flowinguninterrupted circuit exists at all points in the system. In FIGURE 4 novalve at all is used.

As an example of temperatures which may be achieved with a device of thetype shown in FIGURE 3, assuming heat exchanger 14 is maintained at 70F., it is possible to cool heat exchanger 14a to 200 F. and lower` Thismay be accomplished in a matter of a few minutes or somewhat longerdepending upon the diameter of the tube used and the cycles per minuteof the pressure oscillation. When a heat load Q member is attached toheat exchanger 14a, heat will be removed from the heat load member andit will be cooled. It should be noted that temperatures of -200 F. andlower may be achieved with relatively s-mall compression ratios andrelatively high thermal efiiciency may be achieved.

In the multi-stage type of apparatus of the invention shown in FIGURE 4the temperature drop ratio achieved in the single stage unit may bemultipled. By means of a multi-stage unit, as shown in FIGURE 4, one canstep the temperature down from that achieved by a single stage unit toany temperature in which a thermal regenerator can operate, i.e., l0l5K. A two-stage unit can readily achieve 80 K. and a little lower in somecases; a three-stage unit can achieve 40 K., etc.

The heat exchanger 14a and its associated heat load Q, together with theregenerator 20, may preferably be insulated to prevent extraneous heatleak to thus cause a parasitic heat load on the refrigerator. Theinsulating effect may be accomplished by any standard insulatingmaterial or a high vacuum enclosure or in other ways.

Similarly, the invention is not limited the specific form of gascompressing means disclosed, but may be embodied in a system wherein thegas volume is moved by other types of displacement mechanisms than thoseshown in FIGURES l, 3 and 4.

In place of the sintered metal, I may desire to accomplish flowsmoothing of a gas in other ways as, for example, by means of a discformed with very fine holes arranged to form substantially uniformlysized passageways. For example, a comminuted mass of non-metal materialcoated with a binder may be processed to form a smoothing flow body.

Various other changes and modifications may be resorted to within thescope of the appended claims.

I claim:

l. Method of refrigeration which comprises supplying gas along a path offree flow through a thermal regenerator and a iirst heat exchanger andthrough a porous body to achieve llaminar flow as it moves then into oneend of an enclosed gas filled volume thereby compressing the gas alreadyin the said gas filled volume and causing a continuous increase intemperature in all the gas while it is being supplied and as it iscompressed into the opposite end of the enclosed volume, removing heatfrom said gas in a second heat exchanger at the said opposite end ofsaid enclosed volume at a temperature higher than the temperature of thegas entering said enclosed volume and leaving said first heat exchanger,then expanding said gas in said enclosed volume thereby to cause aprogressive decrease in temperature as the compressed gas expands awayfrom the said opposite end of the enclose volume and discharges throughthe said first heat exchanger and regenerator, and adding heat from arefrigeration load located adjacent to the said lirst heat exchanger tothe exhausting gas as it passes through said first heat exchanger in anamount equivalent to the said heat removed from the gas in the saidsecond heat exchanger and at a temperature lower than that of the saidsecond heat exchanger.

2. A refrigeration method which comprises varying the pressure in anenclosed gas iilled fixed volume by introducing and removing gas fromone end of the gas filled fixed volume through a regenerator along afree flowing path while inducing temperature changes as the gas isremoving heat at a heat sink temperature at an opposite end of the gasiilled volume and adding heat from a refrigeration load imposed adjacentto said first end of the gas filled volume at a temperature lower thanthe temperature of the said heat sink temperature.

3. Method of refrigeration which comprises supplying gas continuously ina free flowing uninterrupted path through a thermal regenerator and afirst heat exchanger at one end of an enclosed gas filled fixed volumethereby compressing the gas already in the gas filled fixed volume andcausing an increase in temperature in the said gas filled volume at thepoints Where it is compressed into the opposite end of the gas filledvolume, then removing heat from said gas in -a second heat exchange atsaid opposite end of said gas filled volume and at a temperature higherthan the temperature of the said first heat exchanger, and exhaustingsaid compressed gas through said iirst heat exchanger and absorbing heatat the point of exhausting.

4. A method according to claim 1 in which the gas is confined in aplurality of volumes each of which function in a progressive manner suchthat heat is pumped from one volume to another and successively lowertemperatures are achieved.

5. Method of refrigeration which compr-ises increasing and decreasingthe pressure of gas in an enclosed volume by supplying and exhaustinglgas from -an entrance end of the volume through a thermal regeneratorsuch that when pressure is low heat is transferred from the walls of thevolume to the gas and when pressure is high heat is transferred from thegas to the walls at points further away from the entrance and exhaustingend of the volume, whereby heat is pumped away from the entrance endagainst a large temperature gradient in which the flow is in a laminarflow pattern and the laminar flow pattern is achieved by moving the gasthrough `a multiplicity of substantially uniformly sized openings.

6. Method of refrigeration which comprises increasing and decreasing thepressure of gas in an enclosed volume by supplying and exhausting gasfrom an entrance end of the volume through a thermal regenerator suchthat when pressure iS 10W heat is transferred from the walls of thevolume to the gas and when pressure is high heat is transferred from thegas to the walls at points further away from the entrance and exhaustingend of the volume, whereby heat is pumped away from the entrance endagainst a large temperature gradient in which the flow is in a laminarflow pattern and the laminar flow pattern is .achieved by moving the gasthrough a multiplicity of .substantially uniformly sized openings whichare comprised by a sintered metal disc.

7. In a method of the class described the steps which include containinga volume of gas ina tubular enclosure, introducing into the tubularenclosure another volume of gas which is directed along paths of flowextending substantially parallel to the longitudinal axis of the tubularenclosure, compressing the volume of gas already in the enclosure bodythereby to increase the gas temperature, inducing a iiow of heat fromthe compressed gas through the walls of the tubular enclosure at one endthereof, then expanding all of the gas in the tubular enclosure to lowerits temperature and exhausting portions of the gas from the tubularenclosure thereby to induce a ow of heat from the tubular enclosure tothe gas at points of emission from the enclosure.

8. In a method of the class described, the steps which includecontaining a volume of gas in a tubular enclosure having -at one endthereof gas passageways which extend parallel to the longitudinal axisof the tubular enclosure, supplying another volume of gas under pressurethrough a thermal regenerator and then through the said gas passagewaysto cause the gas to enter the tubular enclosure along paths of flowwhich are substantially parallel to the axis of the enclosure,compressing the gas already in the enclosure body and inducing anincrease in temperature whereby heat is pumped from the tubularenclosure.

9. A device of the class described comprising tubular enclosure meansfor supplying gas under pressure through a thermal regenerator and flowsmoothing heat exchanger comprising a porous ga-s permeable body to thetubular enclosure at one end thereof, means for removing heat at the farend of the enclosure to produce heating.

10. A device of the class described comprising tubular enclosure meansfor supplying gas under pressure through a thermal regenera-tor andlflow smoothing heat exchanger to 'the tubular enclosure at one endthereof, means for removing heat at the far end of the enclosure toproduce heating and means for absorbing heat in the flow smoothing heatexchanger to produce cooling at relatively low temperature.

11. A structure as defined in claim 10 in which a heat load is connectedto the said flow smoothing heat exchanger.

12. A structure as dened in claim 10 in which the ow smoothing heatexchanger comprises a cylindrical body having a passageway extendingthrough one peripheral side of the body to communicate with a chambertherein, a sintered metal disc supported on said -member and a pluralityof passageways for permitting circulation of gas entering the peripheralpassageway to move into contact with the sintered metal disc and passtherethrough.

13. Method of lrefrigeration which comprises increasing and decreasingthe pressure of gas in an enclosed volume by supplying and exhaustinggas, owing through a porous body to produce essentially laminar ow, froman entr-ance end of the volume through a thermal regenerator such thatwhen pressure is low heat is transferred from the walls of the volume tothe gas and when pressure is high heat is transferred from the gas tothe Walls at points further yaway from the entrance and exhausting endof the volume, whereby heat is pumped away from the entrance end againsta large temperature gradient.

References Cited by the Examiner UNITED STATES PATENTS 1,321,343 11/1919Vuilleumier 62--88 1,45 9,270 6/ 1923 Vuilleumier 62-88 2,867,973 1/1959 Meyer 62-6 3,101,596 8/1963 Rinia 62-6 WILLIAM I. WYE, PrimaryExaminer.

1. METHOD OF REFRIGERATION WHICH COMPRISES SUPPLYING GAS ALONG A PATH OF FREE FLOW THROUGH A THERMAL REGENEATOR AND A FIRST HEAT EXCHANGER AND THROUGH THEN POROUS BODY TO ACHIEVE LLAMINAR FLOW AS IT MOVES THEN INTO ONE END OF AN ENCLOSED GAS FILLED VOLUME THEREBY COMPRESSING THE GAS ALREADY IN THE SAID GAS FILLED VOLUME AND CAUSING A CONTINUOUS INCREASE IN TEMPERATURE IN ALL THE GAS WHILE IT IS BEING SUPPLIED AND AS IT IS COMPRESSED INTO THE OPPOSITE END OF THE ENCLOSED VOLUME, REMOVING HEAT FROM SAID GAS IN A SECOND HEAT EXCHANGER AT THE SAID OPPOSITE END OF SAID ENCLOSED VOLUME AT A TEMPERATURE HIGHER THAN THE TEMPERATURE OF THE GAS ENTERING SAID ENCLOSED VOLUME AND LEAVING SAID FIRST HEAT EXCHANGER, THEN EXPANDING SAID GAS IN SAID ENCLOSED VOLUME THEREBY TO CAUSE A PROGRESSIVE DECREASE IN TEMPERATURE AS THE COMPRESSED GAS EXPANDS AWAY FROM THE SAID OPPOSITE END OF THE ENCLOSE VOLUME AND DISCHARGES THROUGH THE SAID FIRST HEAT EXCHANGER AND REGENERATOR, AND ADDING HEAT FROM A REFRIGERATION LOAD LOCATED ADJACENT TO THE SAID FIRST HEAT EXCHANGER TO THE EXHAUSTING GAS AS IT PASSES THROUGH SAID FIRST HEAT EXCHANGER IN AN AMOUNT EQUIVALENT TO THE SAID HEAT REMOVED FROM THE GAS IN THE SAID SECOND HEAT EXCHANGER AND AT A TEMPERATURE LOWER THAN THAT OF THE SAID SECOND HEAT EXCHANGER. 